1. Field of the Invention
The present invention relates to an electronic timepiece having a transmission wheel rotation position detecting unit which detects the position in the rotation direction of a transmission wheel of the electronic timepiece contained in a wheel train thereof such as an obverse wheel train or calendar wheel train.
2. Description of the Prior Art
In a conventional electronic timepiece, as illustrated in FIG. 38, a part of an obverse wheel train 930, e.g., a 24-hour contact point 932 for detecting a rotational position of the obverse wheel train 930 is provided on an hour wheel. When the 24-hour contact point 932 detects the position corresponding to the time of twelve o'clock at night, according to a detection signal output from the 24-hour contact point 932 a circuit block 934 rotates a date driving motor 936. Due to the rotation of the date driving motor 936, a date dial 912 is rotated through a reduction wheel train 938. This makes it possible to change the display of the date.
In the above-described conventional electronic timepiece, in a region near to an outer-peripheral portion of a gear portion of the hour wheel there was provided a conduction pin. And, it was arranged that when the hour wheel rotated, the conduction pin moved a contact point spring so as to cause this contact point to contact with a contact point pattern of the circuit block, and that, when the hour wheel further rotated, the conduction pin was moved away from the contact point spring with the result that the contact point spring was moved away from the contact point pattern of the circuit block. Namely, the contact point spring corresponds to the 24-hour contact point 932 and it was arranged that when the contact point spring contacted with the contact point pattern of the circuit block, the position corresponding to the time of twelve o'clock at night was detected.
Also, in a structure wherein the date driving wheel was rotated through the rotation of the intermediate date driving wheel by the rotation of the date driving motor and the date dial was rotated by the rotation of the date driving wheel, the tooth configuration of the respective gears of the intermediate date driving wheel, date driving wheel and date dial was constituted by a circular arc tooth configuration that includes one or more circular arc portions.
Accordingly, when an external force such as an impact had been applied to the date dial, the rotation of the date dial was stopped by only the index torque of the date driving motor.
However, in the conventional electronic timepiece, there were the problems which follow.
(1) Since the contact point spring was formed of material which was easy to flex, the portion of the contact point spring which contacted with the contact point pattern was difficult to position.
(2) In order to dispose the contact point spring having a sufficient spring length, a significantly large space was needed in the electronic timepiece. (3) When the portion of the contact point spring which contacts with the contact point pattern is disposed at a position which is farther away from the contact point pattern than necessary, even when the hour wheel rotates, the contact point spring cannot be contacted with the contact point pattern of the circuit block by the conduction pin, with the result that time display or calendar display becomes unable to be accurately made.
(4) When the portion of the contact point spring which contacts with the contact point pattern is disposed at a position which is nearer to the contact point pattern than necessary, when the hour wheel has rotated, the pressure of the contact point spring applied to the conduction pin becomes high, with the result that there is the likelihood that any inconvenience will occur in the operation of the electronic timepiece or the electronic timepiece will inconveniently stop.
(5) The structure of the hour wheel becomes complicated with the result that it becomes necessary to use the contact point spring having a sufficient spring length.
(6) In the conventional calendar equipped electronic timepiece provided at a part of the obverse wheel train with the 24-hour contact point for detecting the rotation position of the obverse wheel train, since a number of wheel trains were disposed between the obverse wheel train and the date dial, it was difficult to achieve an accurate positional coincidence of the date dial due to the backlashes between two adjacent ones of the respective wheel trains.
(7) It was difficult to enhance the precision with which the position in the rotation direction of the hour wheel was detected.
(8) There was the possibility that when an external force such as an impact had been applied to the electronic timepiece, the indication wheel or date dial would rotate. In order to prevent the resulting positional displacement of the date dial, it was needed to increase the index torque of the motor (the stationary force: the torque that resists the rotation when at rest). However, when increasing the index torque of the motor, it resulted that the electric power needed when driving the motor also became increased and as a result the battery life of the electronic timepiece was decreased.